I bought over a very mint looking, scratch-free, user-mark-free lens from someone who bought first hand in Nov 2011 from Hong Kong with 1 year Sigma International warranty. Tested on the spot was ok. Paid cash and placed it in the car boot. In the evening, I got off from work and after dinner, took out the lens to mount it and lens could hardly autofocus and took 10s to focus on anything. Next morning, i brought it to Sigma Marketing in Singapore and surprisingly, the lens started autofocusing.
Intermittence issues I guess with the HSM. Was quoted $170 to replace the lens barrel that housed the HSM unit.
Thank goodness the seller agreed to foot $125 of the repairs whilst I did all the leg work. Took only 3 business days to repair and the lens is now as good as new, cleaned, re-calibrated.
Performance-wise, lens is super sharp, produces pics with a 'wow' look from that super creamy bokeh with a '3D' pop. Lens focuses way faster on my 6D than the Canon 85 f1.2L v1 (keg I) I first had in 2007 and on my 1dmk2, i mean really way faster.
At just slightly more than 1/3 the price of the Keg II, I would take this lens anytime over the Canon, which i missed a lot of shots indoors due to the AF.
Picture quality-wise, the Keg I's bokeh equal if not just slightly better. Sharpness-wise, the Sigma is sharper at 1.4 than Canon at 1.2, but slightly.
The Sigma does produce warmer colors out of cam and I need to correct the green color channel vs the Canon's more neutral colors.
But for the cost, practical use, the Sigma wins hands down and my heart. Perhaps it has won me over to consider the Sigma 35 f1.4 ART over the Canon 35L.